The present invention is a continuation of International Application PCT/SE2004/001509, filed Oct. 19, 2004, which claims priority to SE 0302834-7, filed Oct. 19, 2003, both of which are incorporated by reference.
The present invention relates to a cooling system for an internal combustion engine mounted in a vehicle, which cooling system comprises a flow circuit with a pump for circulating coolant via ducts in the cylinder block of the engine and a radiator, which flow circuit is separated from atmospheric pressure.
In conventional cooling systems for an internal combustion engine mounted in a vehicle, use is made of a relatively large expansion tank as a reserve volume for coolant and in order to compensate for the expansion of the coolant which takes place when it is heated up from cold starting to full operating temperature, around 80–90° C. The expansion tank requires space and encroaches on the cooling area.
The development of heavy-duty, turbocharged diesel vehicles, for example trucks, has meant an increasing demand for cooling capacity for oil coolers for engine and gearbox, charge air coolers, coolers for EGR gas and coolers for retarders. Some of these devices, for example charge air coolers, EGR coolers and transmission coolers, often require a lower temperature of the coolant inflow than that required by the internal combustion engine.
This demand has usually been met by increasing radiator area and coolant flow. These measures generally mean that the risk of cavitation at the coolant pump increases because the pressure drop in these cooling systems is great.
From U.S. Pat. No. 6,532,910, for example, it is known to pressurize a cooling system via the expansion tank by means of positive pressure from the intake side of the engine. The pressure increase means that a higher temperature can be maintained in the cooling system, at the same time as the cavitation risk decreases. One problem with this known solution is that it can take several minutes from the engine being started until the pressure in the cooling system has been built up, if the engine is run at low load. During this period of time, cavitation in the cooling system circulation pump and cylinder liners can lead to local overheating which may involve engine damage. Moreover, the system pressure can disappear in the event of minor valve leakage.
It is desirable therefore to produce a cooling system which makes more rapid pressure build-up possible, which can be designed in a space-saving way and with a low pressure drop and which does not lose the system pressure in the event of moderate valve leakage.
According to an aspect of the present invention, a cooling system for an internal combustion engine mounted in a vehicle comprises a first flow circuit with a pump for circulating coolant via ducts in a cylinder block of the engine and a radiator, the flow circuit being separated from atmospheric pressure, and a second flow circuit comprising a coolant reservoir with a normal pressure which is lower than a pressure in the first flow circuit, and a pump for circulating coolant via a pipeline between units with a cooling requirement and a second radiator, wherein the second flow circuit is connected to the first flow circuit via a one-way valve opening in a direction of the first flow circuit.
This design of the cooling system can allow the two flow circuits to be optimized individually for different tasks/temperature ranges with advantageous flow resistance. The flow circuit operating with a higher temperature range can be designed to be closed to the atmosphere, so that the pressure build-up in this circuit can take place rapidly. Normal pressure means the pressure which normally arises in the second flow circuit when the engine operates.